For example, cooling devices of the kind specified are used in vehicles to retain the transportation compartment of the vehicle, and the goods transported, at low temperature. Conventionally a cooling device comprising an elongate housing is utilised, which may be mounted in the roof of the transporation compartment and which is filled with a eutectic liquid (conventionally comprising brine) and through which a cooling pipe extends. During charging of the cooling device a cooling liquid is fed through the cooling pipe from a refrigeration device to freeze the eutectic liquid, which then absorbs heat from the transporation compartment over a period of time to retain the transportation compartment at a desired temperature.
It will of course be appreciated that the nature of the eutectic liquid is selected so as to retain the transportation compartment at a desired temperature determined by the freezing/melting point of the eutectic liquid.
Whilst conventionally such cooling devices have been of metal, it has more recently been appreciated that plastics provides a highly desirable material for the elongate housing. A known method of manufacturing such cooling devices involves the use of a housing in the form of an extrusion of generally rectangular cross-section, into which a cooling pipe is located and on to which end caps are secured. Desirably, however, the cooling pipe enters and exits the housing at the same end, with the pipe extending as an elongate "U" within the housing. Thus the extrusion is of non-square rectangular cross-section. During the extrusion of such a housing there is a tendency for the side walls of larger width to collapse inwardly. Consequently it has become conventional practice to utilise as a housing for a cooling device of the kind specified an extrusion having a web interconnecting the opposite side walls approximately centrally thereof. However, the utilisation of such a web has the disadvantage, that it does not permit any significant increase in the volume confined by the housing under differential expansion, and it may be necessary to fill the housing with eutectic liquid to an extent less than 100%, to provide space for such differential expansion.
Difficulty is also encountered in cooling devices using extruded housings in the supporting of the cooling pipes, particularly during differential thermal expansion, and in practice it has been found necessary to utilise spacer elements on the pipe which engage with the walls on the housing compartments. This however restricts free-flow of the eutectic liquid within the housing, and localised areas of eutectic liquid may result which are surrounded by plugs of frozen material. This under certain circumstances can cause damage to the housing.
Another difficulty which has been encountered is that, in cooling devices of the kind specified, it is on the one hand desirable to utilise steel as cooling pipework, but to utilise brass connections on the housing by which the device may be connected to a refrigeration unit. However, in use, electrolytic action of the brine causes damages at the junction between the steel and brass. For this reason it is in general necessary to utilise copper for the cooling pipes.